Coiled lamp filament



Aug. 9, 193 s. WADSTEN ET AL 1,871,018

COILED LAMP FILAMENT Original Filed Dec. 29, 1928 INVENTOR 5. M44295 TE/V ATTOR E I Patented Aug; 9', 1932 UNITED. STATES PATENT ori-l cs ms wansrmr, or BLOOMFIELD, AND cmnns WALLACE HUNT, or wyomtue,

NEW

I JERSEY, ASSIGNORS '10 WESTINGHOUSE LAMP COMPANY, A CORPORATION 01' Pm- SYLVANIA f I 001mm murmur Original application filed December 29, 1928, Serial No. 329,149. Divided and this application. med October 30,1829. Serial No. 403,886.

This invention relates to the manufacture of incandescent electric lamps and is a division of application Serial No. 329,149 filed December 29, 1928 relatin to the production 5 of a coiled filament of defihite length for use in saidlamps.

Incandescent electric lamps may be generallydivided into two classes, first those employing a straight or uncoiled filament and secondsuch lamps as employ a light source consisting of a fine filamentary wire wound into helical form. The present invention is concerned with the last mentioned type of filament which is generally known in the art" as the concentrated type, the same being adapted for use in either :a gas filled or evacuated bulb.

The coiling of a lamp filament to produce a light source is an important and exacting op-.

2 eration and it has been the practice to employ two methods of winding. First the method of winding a filamentary wire upon a mandrel, cutting. the mandrel containing helix into definite lengths or sections immersing the sections in an acid bath to dissolve the mandrels and subsequently dipping the mandrelless coils in acleaning solution. The second method consists in coiling a filamenta'ry wire to helical form in the absence of a mandrel, in which case it is'only necessary to dip the filaments in the cleaning solution.

lVhen producing a light source or sectionof filament for use in a lamp of a ven wattage certain conditions must be care ully observed and strictly adhered to. The length of the selected filament wire contained in the light source must be exact so that the proper resistance will be obtained for a given wattage 'lamp. Each given length of wire must be contained in a helix of a given number of turns, the pitch of the helix must be maintained uniform and the outside diameter of the. helix held constant 1- It has been found practical to me'etthe above requirements on the mandrel coil winding machines and especially on a mandrelless coil winding machine shown in Patent 1,670,499 in. which a filamentary Wire is wound to helical form in the absence of a mandrel and automatically cut into'sections,

each section containing equal lengths of wire.

Although the above mentioned mandrelless coil windi'n machine may operate to meet all the requirements of the:rating data, that is, in providing the proper diameter, pitch and length of wire contained in a coiled section, it'does not follow that all the coiled sections are of the same overall length.

In winding of filaments on a mandrel the filaments may be cut to a* definite length while on the mandrel, but 'when removed therefrom the release of internal tension or other force results in the production of filamentsalthough containing equal lengths of wire still possess differences in their over-all lengths. A It is an object of the present invention, therefore, to produce a coiled filamentary body which will meet requirements as to diametrical dimensions, pitch and length of w1re contained in a coiled section and at the same time have uniform over-all lengths.

Another object of the invention is to provide lamp filaments consisting of coiled sections of equal over-all lengths.

Another object of the invention is to provide a method of producing coiled filamentary sections having uniform over-all lengths and in treating said-sections preparatory t in corporation-in a lamp.

Another object of the invention is to provide a simple'method of setting and cleaning such filaments for use It will be understood that in the manu- I facture of an incandescent electric lamp the internal structure includes a number of glass parts which may comprise an exhaust tube,

a flare tube and an arbor consolidated together by fusion and having sealed in the fused portion a/pair of leading-in wires or conductors. The leading-in wires extend upwardly to the exposed end of the arbor which contains a plurality of what are termed, support wires. These wires have their ends em-. bedded in thea'rbor and extend radially therefrom. The free ends of the support wires are formed with hooks or pig tails to receive and hold a lamp filament and the ends of the filament are secured to ends of the leading-in wires.

. Heretofore the operation of securing the filament to the lead-in wires was performed manually, the operator upon picking up a filament connected one end by clamping or welding to a lead-in wire then inserted the filament into the support wires and finally connected the other end of the filament to the other lead-in wire or conductor. In performing this operation it was possible for the operator to slightly adjust the lead-in wire in case .the filament was too long or too. short. 7-

In the automatic application of a filament to leading-in conductors, however, it is necessary to position the conductors-in a definite spaced relation, therefore, unless all filaments possess exactly the same over-all length difliculties arise in that the filamentmay fail to reach the positioned lead-in wire or may over-lap the same.

In the first case the mounting operation will be a failure while in the second case a section oi the filament will be short circuited changing the rating of the lamp.

In accomplishing the object of the present invention a filament may be wound on a coil winding machine, but instead of winding the coil in the form of a helix having the turns in spaced relation the coil may be wound in what is termed, a tight winding, that is each turn would be in contact with the adjacent turn or with no space existing therebetween. when so wound the coil may be cut into sections of given lengths which may be designated as the cutting lengths and then stretched so as to space the turns of the coil to such degree as to make the over-all length of the coiled section a given dimension. Coils of this character may then be employed in connection with an automatic mounting operation since all the coiled sections have a'given over-all length.

On the other hand the same result may be obtained by winding the coils on a coil winding machine with the turns in spaced relation,

but with a. greater number of turns per inch, or unit of length and with a slightly larger outside diameter than specified for the coil when used as a light" source. The coil may then be stretched to a specified length or specified number of turns per inch and a given diameter, thus giving the coils a uniform over-all length and at the same time maintaining the proper length of wire in the coil.

In practicing the method for preparing coils for automatic mounting'operation, it has been found'that certain advantageous steps are possible,

os1tion after stretching they may be flashed an electric current either in the air or an cable to since while the coils areheld in inert gas. When flashed in air the carbon or other foreign material clinging to the wire is oxidized and the subsequent flashing in an inert gas serves to remove the oxide and flash off any remaining foreignsubstance or to reduce any tun sten oxide that may be present.

From the oregoing it will beevident that the present invention contemplates a method of producing filamentary bodies to serve as coil practical for use in connection with the automatic mounting of the coil.

The invention will be more fully under stood from the accompanying drawing which diagrammatically represents the steps of the method and its relation to the automatic mounting of the filament.

Fig. 1 shows a diagrammatic representation of a coil winding die with driving rollersto propela wire for formation into a helix.

Fig; 2 shows a coiled Wire as itissuesfrom a die and moves in position to be severed by cutting knives, the coil shown is greatly exaggerated in-size for the purpose of. clearness.

Fig. 3 shows a section of coiled wire cut from a continuous length.

Fig. 4 shows the section of coiled wire illustrated inFig. 2 but stretched to a given len h.

1g. 5 shows the wire disposed in a chamber containing an 1nert gas in which the coil may be heated.

Fig. 6 shows a. length of coiled wire stretched to length, heated and cleaned ready to be applied to a lamp stem in this view the coiled section more nearly approaches the proportions of the actual filament.

Fig. 7 is a plan View of a stem with the filament mounted thereon and illustrates the definite position of the leadingin wires and Fig. 8 is a side view of a portion of a lamp stem having a stretched filament applied thereto. i

Althou h the present invention is applifilaments wound on a mandrel the present example of one embodiment of the in vention applies to coils woundin the absence comprise a die 10 supported in a holder l1.

A pair of upper and lower driving or force rollers 12 and 13 frictionally' engage a wire 14 and move the same endwise into the die which is rovided with a coil bending cavity.

15. At t e edge of the cavity is a lip (not shown) .which operates to space the turns of the coils as they issue from the die. The

pitch of the coil maybe varied by' changing.

stretched length of coiled the relative position of the die with respect to the driving rollers .and if an extremel tight or close turned wound coil is desired the spacing lip may be omitted although a tight wound coil may be produced by a d e with a. lip by proper adjustment of the die with respect to the direction of movement of the wire under the action of the driving rollers.

Machines for winding coils in accordance with the above are known to those skilled .in the art and a continuous length of helically coiled wire of a given pitch may readily be obtained.

As the wire 14 is wound it issues from the die in the form of a continuous helix 16'as shown in F ig 2 and may pass through aguide 17 and between cutting edges 18 and '19, which serve to sever a section 21 of a, given length.

- In the mandrelless coil winding machine above referred to the severed coiled section 21 contains a predetermined amount of-wire, since in accordance with the operation of the machine the cutting knives are operated through the agency of a measuring drum so arranged that when a given point on the wire travels through a given distance the cutters operate thus the severed section always contains a given amount of wire. v

If slight variations in the pitch and diameter of the coil exist however, the over-all length of the sections may var The overall length of the sections may be construed as the length of the body of the coil from end to end indicated by the letter A77-'v In accordance with the present invention a continuous coil may be wound with the pitch of the turns relatively close or with a greater number of turns per unit of length than desired in the'section when secured to a stem as shown in Fig. 2.

The section 21 may then be severed and the ends gripped between pairs of jaws 22 and 23. When so held the pairs of jaws ma be separated a given distance to stretch the section to increase its over-all length, indicated as B, and thus reduce the number of turns per unit of length giving a section 24 as shown in Fig. 4e.

In determining dimension B the mounting of the filament is considered and as shown in Figs. 7 and 8 a stem 25 may be taken as in position to have a filament automatically applied thereto. The stem shown comprises'a press 26 from which an arbor 27 extends.

- v The free'end of .the arbor is provided with ceive" and retain i lation by pairs of jaws 33 and 34 thus the era button 28 having support wires 29 extending therefrom. The exposed ends of the sup-. port wires having hooks or pig tails to re-' the filament. Leading-in wires- 31 and 32 are held in definite fixed redistance Bjor over-all length of the filament what is termed black wire cant such as aquadag .-draw1ng operation.

v eter may beemployed.

section must be such that ends 35 and 36 will y lie in position on the leading-in wires when the filament is disposed in its circular position in the support Wires. The. circumferential dimension of. the filament when on a stem must therefore be equal to B without changingthe number of turns per unit of length in the coiled section. When filamentary sections are produced by the above described method they may either be carried by the jaws 22 and 23'to position for attachment to the leading-in wires or a quantity of such filamentary sections may be fed to mechanism which will automatically mbunt the filament on the support wires to be secured thereto by welding or clamping as desired.

The present invention however, further contemplates the step'of cleaning the filament. It is well known that when using difiiculty is encountered in cleaning the coils, Black wire consists of drawn tungsten in which a lubriis used during the This lubricant adheres to the wire and if not removed is detrimental to the life of a lamp in which the filamentmay be incorporated. Heretofore the coils or filaments were cleaned by immersion in sodium hydroxide and a solution of sodium bichromate.

It has been found that when practicing the present method it lends itselffto the step of cleaning sincewhile the coiled sections are eld between the jaws 22 and 23 and stretched they may be moved into a chamber 40 contraining a gas-such as hydrogen or nitrogen or a mixture of suitable gases and electric current may be passed through the filament b means of conductors ll and 42. By this'hea ing of the filament the deleterious substances are destroyed and removed at the same time the filament takes a permanent set.

It has also been found of advantage to flash or heat the filament in air directly after y the stretching operation in which case electric current may be passed through conductors 38 and 39. The air flashing is not essential but may be employed if des1red since it oxidizes the carbonaceous material or makes the same more easily removable when the fila-' ment is flashed in an'inert gas or a final cleaning step; A w

From the foregoing it will be evident that the present method not only provides an a'dvantageous modeof producing filament sec,-

tions of equal over-all length, but combines with this feature the operation of setting and cleanin which may be accompl shed" in an economlc and effective-manner.-. x

hen practicing the present method to produce a filament say for a 60 watt lamp, a tungsten filament wire of 1.85 mils diam- I This wire is'coiled into a continuous helix having an outside diameter of about 10.8 mils and having 390 turns per inch. A section equal to A is then severed and stretched about 5% to give a section having 370 turns er inch and an over-all dimension equal'to B.

It is understoodthat the dimension A is a determined dimension and selected so that when the filament is stretched the 'dimension B will be'such that the ends of the coiled section will take their proper positions on the leading-in conductors which are in a given fixed relation for the type oflamp in' which the filament is to be used. I

The above description gives as a practical example of the invention, the initial winding of a spaced coil having a greater number of turns'per unit of length than the final coil. The initial coil may, however, as hereinbefore mentioned, be wound with the turns in contact and subsequently stretched and flashed. When winding a coil with the turns in contacting relation on the mandrelless coil winding machine, for example, an advantage is gained in that thelip of the coil winding die may be omitted to the end, that the construction of the die is simplified. This is important since coil winding dies are generally made from a diamond and if the construction can be made less com licated the cost of producing such dies'is re need and by reason of the absence of the lip there is less danger of breakage.

Certain advantages are present with both modes of procedure-in carrying out the present method and it is evident that the underlying idea of the production of an initial coil of a greater number* of turns per unit of length stretched to acoil of a desired numberof turns per unit of length is common to either the tight wound or the spaced coil mode of procedure. Furthermore a filament pro- I duced in accordance with the above method possesses certain properties or novel characteristics which distinguishes it from coils as heretofore produced, as will be evident from the following:

As above set forth a coiled section having a given number of turns er unit of length is severed from acoil of in efinite length: The severed section is then gripped between jaws 22 and 23; These jaws secure a plurality of turns of the coil, these turns which constitute the terminals of the filament are indicated as 43 and 44. Each end is so held that their initial pitch is maintained during the stretching operation. This results in a coil body or section wherein the major or light giving 1. ortion of the filament possesses a lesser number of turns per unit of length than do the It has been found that when holding the ends of the filament between jaws during the heat treatment that the secured portions of the filament'remain substantially cool and thus retain their initial malleability, that is, they are less brittle portion of the filament which has been subjected to a relatively high temperature heat treatment.

It will be understood that the ends of the filament are secured to leading-in conductors, the ends of which are usually bent over and clamped upon the end-pf the filament. By making the jaws 22 and23 of slightly greater width than the width of the clamps at the end of the conductors the unheated portions or terminals of the filament will be of'sufficient length to extend slightly from the side of the clamp of the leading-in wires or conductors thus giving a turn or Half a turn of pliable wire 45 adjacent to the clamping point. A filament so constructed tends to resist breakage due to vibration and since it has been found that in a lamp filament the 1 portion of wire adjacent to the clamp is subjected to severe strain and since the present construction serves to improve the strength of this portion of the filament, a new and decided advantageous result is attained.

Furthermore, during the clamping operation it is necessary in order to properly secure fductor. In a filament such as produced by the present method the'terminals being pliable. or free from brittleness are more readily clamped without breaking away from the main portion of the filament.

'Whensecnring the terminals of the filament between jaws during the stretching and subsequent heat treatment, the portion held by the jaws obviously do not receive the same degree of cleaning as the main portion of thefilament. In ractice it has been found that no detrimenta effects result from this absence of cleaning at the terminals since when the filament is mounted on a stem the terminals remain relatively cool. If necessary, .however, the filament may be given an additional cleaning step by dipping in any suitable cleaning solution known to the lamp-making art.

It will be understood that although a filament having terminals offgreater strength than the main body of the filament are advantageous with a clamping operation they will also bedesirable if the ends of the filament are to be welded or otherwise secured to the leading-in conductors. Since in this case as in the clamping, a sufiicient amount of the pliable portion of the ,wire may be disposed between the clamped portion'and the light giving portion.

It is to be understood that the above is only of turns per unit of length at its terminal portions. being of t portions said terminal greater pliability than the turns of said major portions.

In testimony whereof, We have hereunto subscribed our names 1929.'

STEN WADSTEN. CHARLES WALLACE HUNT.

this 28 day. of October, 

